With the development of electronic technologies, power conversion circuits are increasingly widely used. For example, referring to FIG. 1, a traditional power conversion circuit 100 includes an upper switch G1, a lower switch G2, an inductor L, a load resistor R1 and capacitors C1, C2 and C3. When the circuit normally works, the upper switch G1 and the lower switch G2 are turned on complementarily.
For a power conversion circuit similar to what is shown in FIG. 1, when a scram event such as overcurrent, overvoltage and overheat protection occurs, in the traditional protection method, the upper switch and the lower switch are turned off no matter what the direction of current is.
When the switch is a reverse conducting-type semiconductor switch such as a silicon carbide MOSFET, a parasitic reverse diode therein generally has a relatively high conduction voltage drop; and when a large reverse current flows through the parasitic reverse diode, a great power loss will be generated. Therefore, if a freewheel current of the inductor reversely flows through the parasitic diode of either of the upper switch and the lower switch, the parasitic diode may suffer from relatively large power loss and thermal stress, and even will be burnt in a severe case.
For this reason, one solution generally adopted is to reversely connect a high-performance diode in parallel to the switch. As the conduction voltage drop of the diode is relatively low, the reverse current will flow through the diode, so that the parasitic diode is prevented from generating reverse conducting loss and thermal stress when the switch is turned off. However, using this method may additionally increase material cost and manufacturing cost. In addition, another solution generally adopted is to employ a semiconductor switch with a larger current specification, and also a highly sensitive protective detection circuit is provided, so that when a circuit or system break down, a control circuit proceeds a rapid detection and a protective action is triggered to turn off the semiconductor switch as early as possible, thereby avoiding the problem of severe occurrence of overcurrent or overheat. However, using this method may enhance requirements for protection and detection circuits and costs of the semiconductor switches. Therefore, it is still required to develop a method giving consideration to normal operation and scram protection of the power conversion circuit and limiting thermal stress.
It is to be noted that the above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.